The proposed project is a continuation of an ongoing research grant for the isolation of sperm membrane autoantigens. This project will biochemically characterize the rabbit sperm membrane autoantigen (RSA-1), isolated during the first grant period, including amino acid analysis, carbohydrate content, and carbohydrate-protein linkage. Specific antibodies to RSA-1 will be made and used for determining antigen binding sites, ultrastructural localization during sperm penetration to the egg and antifertility effects during in vitro fertilization. A second autoantigen will also be isolated during the proposed project using the methodology established for RSA-1.